ABB H&B Publication 60-0.15 EN

ABB H&B Publication

Certain industrial processes or applications necessitate controllers which satisfy safety engineering requirements. For instance, heat generating plant which is heated with fluid, gaseous or solid fuels requires controllers which meet the requirements of DIN 3440 [6]. This also holds for controllers used in heat-generating or heat-transfer plant which, irrespective of the type of heating energy, heat a thermal transfer medium such as water, steam, oil or air. Land-type boiler systems must use water-level controllers which meet the specifications of VdTÜV Data Sheet No. 100/1 [7] and thereby satisfy the requirements of the "Technical Guidelines for Steam Boilers" (TRD). Controllers with corresponding approval are also required for boiler plant with only limited or periodic monitoring. Controllers used on sea-going or inland waterway vessels, or in offshore facilities, have to satisfy the requirements of Germanischer Lloyds. Hartmann & Braun controllers satisfy these requirements.

Matching the controller to the controlled system Matching the control parameters Xp, Tn and Td to the control application and the controlled system is often referred to as optimization. However, optimization is a decision process which precedes parameterization. In the optimization phase a decision is made as to whether the controller should – adjust for a set point deviation as rapidly as possible, accepting that an overshoot may result – adjust for a set point deviation without any overshoot – compensate for disturbances in an optimal manner – reach the set point with the lowest power consumption – u. a. m. Once the target has been established, the control parameters can be determined and set on the controller. 3.1 Manual determination and setting of control parameters The parameters Xp, Tn and Td are established for controllers by – trial and error – experience – evaluation, for instance of transfer functions using a rule of thumb or – the use of mathematical methods. PC programmes are used here. These approaches are in general very time consuming and often too imprecise to achieve optimal results at the first attempt. Consequently, there has long been a need for controllers which find their own parameters and adapt themselves. 3.2 Adaptive controllers The term "adaptive controller" is inadequate to describe the function of such a controller. VDE/VDI Guideline 3685 gives more details on the classification of the various options:

"An adaptive control system is one in which characteristics which can be influenced are automatically set to variable or unknown process characteristics so as to elicit an improvement. The terms self-setting, self-adapting and self-optimizing in the sense of this definition are all synonyms for the term "adaptive" [8]. Such an adaptive system is described by reference to Fig. 12: "Identification in an adaptive control system serves to establish the characteristics of a system or part system." "In the decision process, that information received about the identification is compared to th

Realization in H & B controllers Start-up adaptation is realized in H&B controllers under the designation self-parameterization. This simplifies and speeds up the start-up process and leads to better control performance than the usual methods in which exact measurements are often omitted to save time and the parameters are only approximated. Control of the parameters through the set point, the controlled variable or other measured signals is a simple matter with Hartmann & Braun controllers. Since no general approach is possible for such tasks, a special configuration has to be drawn up for such applications by either Hartmann & Braun or the operator. Self-parameterization can be a valuable aid to establishing various parameters for different loading conditions. 

Two interfaces, of equal functional value, are available for different applications. A configuration interface which can be accessed from the front allows the functions parameterization, configuration and feedback documentation to be carried out. The controller itself is generally off line whilst they are being carried out. The computers used for this are mostly portable so that they can be used at different sites. They are connected to the controller via an adapter cable. The rear interface allows the control of one or more units via a bus. Although this interface can also be used for configuration and parameterization, the bus is best used for operational (on-line) functions. For these tasks the computers are generally stationary, with a fixed connection to the controller.

Computer applications Hartmann & Braun offers complete, powerful software programmes for the functions operation and monitoring as well as process visualization, parameterization, configuration and feedback documentation. The applications set point control and direct digital control are in most cases so closely bound to the controlled system that no generally-valid programmes can be written for them. The interfaces, however, are documented such that coupling programmes can be written

Fundamentals of Control Engineering

Set point control through a computer of any design. With such an arrangement, the computer adjusts the set point according to superordinate criteria. These may include the order book situation at any given time, the breakdown of the orders, the power consumption at a given time or any of numerous other criteria. The aim is in most cases to optimize production. – Direct Digital Control. In normal cases control is a task of a superordinate computer. Compact controllers are subordinate to this computer and assume the control function in a bumpless manner if there is a computer fault. The following operating modes are conceivable: Retention of the last computer correction value in manual operation Automatic operation with safety set point Automatic operation with the last value of the controlled variable adopted as the current controller set point (x-tracking) Cascade control. – Operation and monitoring of the system. Important information for operation of the system is displayed in a suitable manner on one or more screens to enable processes to be monitored and changes made if necessary. – Feedback documentation of the parameters set in the controller and any change made to their configuration.

– Process visualization: A powerful software programme, in conjunction with a master computer or PC, makes it simple for a user to centrally operate, monitor, control and automate a process.

Definitions These definitions are extracts in an abbreviated form from DIN 19 226. Where doubt exists, the original definitions are definitive. Analogue signal A signal with a continuous value range. Limiting control A combination of at least one main controller and an additional controller which ensures that the variable to be limited does not exceed predefined alarm values. Binary signal A digital signal with only two values. Digital signal A signal which can assume any one of a finite range of values. Set value control The reference variable is set to a fixed value (which can be changed). Follow-up control The value of the controlled variable follows the changing value of the reference variable. Response to set point changes The response of a controlled system to changes in the reference variable. Limit signal The binary signal of a limit monitor. Limiting value The value of the input variable of a limit monitor at which its binary output signal changes. Manual control Human control of at least one element of a control loop. Cascade control The output variable of the (master) controller forms the reference variable for one or more slave controllers. Configuration The elaboration of a control concept from preconstructed programme modules. Control station Operating mode switches, adjusters for reference and output variables and the necessary display functions are brought together in the control station. Optimization Establishing a quality criterium. Parameterization The assignment of values for the characteristics of the modules of a system Programming Developing, coding and testing of a computer programme. Switching point The value of the input variable of a limit monitor at which its binary output signal changes. Differential gap The difference between the switching points (hysteresis) for which the binary output signal of a limit monitor changes with rising and falling input variables. Actuating time The time taken for the output variable to run through the entire correcting range at maximum speed.

Disturbance variable Any variable acting on a system which disturbs the intended effect. Feedforward control Integration of the measurement of disturbance variables in the control algorithm. Disturbance response The response of a controlled system to disturbances. Structuring a) Analysis Breakdown of a system so that its relationships become visible. b) Synthesis The assembly of a system from functional units so that the requirements are met. Time-programme control The reference variable is changed according to a time-schedule. Cycle time Time interval between two sequential, identical, cyclical recurring processes.

Symbols The symbols below are taken from DIN 19 226. The symbols used in the controllers may differ in some respects for technical reasons. If so, then please refer to the relevant Operating Manual. e Control deviation e = w - x (see also xw or xd) KD Derivative-action coefficient (KD = Tv ⋅ Kp) KI Integral-action coefficient (KI = Kp / Tn) Kp Proportional-action coefficient (see also Xp) Ks Controlled system gain (transfer coefficient) r Feedback variable (derived from x) S Controlled system t Time (operating) Tg Recovery time Th Half-life Tn Integral-action time (Tn = Kp / KI) Tt Dead time Tu Delay time Tv Derivative-action time (Tv = KD / Kp) Ut Dead zone USd Differential gap w Reference variable (set point) Wh Range of reference variables x Controlled variable (actual value) xA Object variable XAh Object range xd Error signal (replaced by e) Xh Control range Xp Proportional band (Xp = 1 / Kp) XSd Differential gap (hysteresis) xw Control deviation (xw = x - w) replaced by e, corresponds to deviation from set point y Output variable Yh Correcting range yR Controller output variable z Disturbance variable Zh Range of disturbance variables

Fundamentals of Control Engineering

Bibliography [ 1] W. Oppelt, Kleines Handbuch technischer Regelvorgänge, Verlag Chemie GmbH, Weinheim [ 2] DIN 19 221 Formelzeichen der Regelungs- und Steuerungstechnik [ 3] DIN 19 222 Leittechnik, Begriffe [ 4] DIN 19 225 Benennung und Einteilung von Reglern [ 5] DIN 19 226 Regelungs- und Steuerungstechnik, Begriffe Teil 2: Übertragungsverhalten dynamischer Systeme Teil 4: Regelungs- und Steuerungssysteme Teil 5: Funktonelle und gerätetechnische Begriffe [ 6] DIN 3440 Temperaturregel- und -begrenzungseinrichtungen für Wärmeerzeugungsanlagen DIN 4754 Wärmeübertragungsanlagen mit organischen Flüssigkeiten DIN 57 116 Elektrische Ausrüstung von Feuerungsanlagen DIN 57 631 Temperaturregler, Temperaturbegrenzer und ähnliche Vorrichtungen [ 7] VdTÜV Merkblatt 100/1 Anforderungen an Stetigregler für den Wasserstand an Landdampfkesseln [ 8] VDI/VDE-Richtlinie 3685, Blatt 1, Eigenschaften adaptiver Regelgeräte [ 9] H. Hame: Selbsteinstellende Regler, H&B-Einzelbericht 02/62-3619 DE, 1988. [10] IEC 546 Controllers with analogue signals for use in industriel process control systems [11] VDI/VDE 2189, Beschreibung und Untersuchung von Zwei- und Mehrpunktreglern [12] VDI/VDE 2190, Beschreibung und Untersuchung stetiger Regelgeräte